Solar water heater

ABSTRACT

Solar water heater using the phase-change principle including a collector, a condenser, and .[.an accumulator.]. .Iadd.a vapor release drum .Iaddend.joined to form a natural circulation system .[., including a pressure accumulator and a vapor release drum.]..Iadd.. .Iaddend.

BACKGROUND OF THE INVENTION

It has been suggested that heat-transfer from a solar collector to watercan be accomplished by use of a phase-change system in which theoperative liquid is boiled in the collector and condensed inheat-exchange with the water to release the heat of vaporization. Thepressure in the system .[.would be maintained.]. .Iadd.may be limited.Iaddend.at a suitable .[.high.]. level by the use of an accumulator. Ithas been found in practice, however, that although the principle issatisfactory, certain practical considerations prevents such a systemfor operating in the optimum manner. For instance, it has been foundthat there is a tendency for the vapor to be converted to liquid in thetubes connecting the collector to the condenser, thus causing slugs ofthe liquid to pass into the condenser. Since it is the return of theheat of vaporization in the condenser that serves to heat the water inthe optimum manner, the presence of any amount of liquid in thecondenser tubes causes a less-than-effective operation. Also, thepresence of large bubbles in the liquid sets up an oscillatory conditionthat can cause flow of liquid into the condenser, as well as causing avibration of the mechanical elements that can lead to their destructionor to the failure of joints. The phase-change solar heater lends itselfto installation in remote locations, because it is a self-regulatingsystem that needs no electricity or supplemental fuel. However, theinstallation in such areas is difficult because of the necessity forassembling it in the field and providing suitable start-up pressure forthe accumulator. These and other difficulties experienced with the priorart devices have been obviated in a novel manner by the presentinvention.

It is, therefore, an outstanding object of the invention to provide asolar water heater in which very little liquid finds its way into thecondenser.

Another object of this invention is the provision of a solar waterheater which is free of large liquid level oscillations.

A further object of the present invention is the provision of a solarwater heater in which the danger of failure of the elements due to fluidoscillation and mechanical vibration is substantially reduced.

It is another object of the instant invention to provide a solar waterheater which can be installed in the field and in remote locations lessneed for skilled workmanship or electrical power at such a location.

A still further object of the invention is the provision of a solarwater heater which is simple in construction, inexpensive tomanufacture, and which is capable of a long life of useful service witha minimum of maintenance.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

SUMMARY OF THE INVENTION

In general, the invention consists of a solar water heater, making useof phase-change heat transfer and having a condenser with an inlet andan outlet, which condenser is in contact with the water to be heated.The solar collector is provided having a bottom inlet and a top outletand having an inner conduit that connects the inlet and the outlet. Theconduit is suitable for exposing a heat-transfer medium in the conduitto solar energy and the collector outlet is located below the condenser.Conduits are provided to join the outlet of the condenser .[.and theoutlet of the condenser.]. to the inlet of the collector .Iadd.and theoutlet of the collector .Iaddend.to the inlet of the .[.collector.]..Iadd.condenser.Iaddend., thus forming a closed circuit containing thephase-change liquid heat-transfer medium. An accumulator having meansfor regulating the pressure .[.is.]. .Iadd.may be .Iaddend.connected tothe circuit below the condenser. A vapor-release drum is connected inthe circuit between the outlet of the solar collector and the inlet ofthe condenser.

More specifically, the vapor-release drum has sufficient volume toassure that the upper surface of the heat-transfer medium always remainswithin the confines of the drum during normal operation of the heater.The drum is of generally elongated cylindrical conformation and extendsparallel to and spaced upwardly from a horizontal upper edge of thesolar collector. This further serves as a manifold connecting theseveral collectors.

BRIEF DESCRIPTION OF THE DRAWINGS

The character of the invention, however, may be best understood byreference to one of its structural forms, as illustrated by theaccompanying drawings, in which:

FIG. 1 is a somewhat schematic view of a solar water heater embodyingthe principles of the present invention, and

FIG. 2 is a vertical sectional view of the heater taken on the lineII--II of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, wherein are best shown the general featuresof the invention, the solar water heater, indicated generally by thereference numeral 10, is shown as using the phase-change principle ofheat transfer. A condenser 11 is provided with an inlet 12 and outlet 13and is in heat conductive contact with a body of water 14 to be heated.The solar collector 15 is provided having a bottom inlet 16 and an upperoutlet 17. The collector has an inner conduit 18 that connects thisinlet and outlet, the inner conduit being suitable for exposing aheat-transfer medium in the conduit to solar energy. The outlet 17 ofthe collector is below the condenser 11.

A conduit 19 joins the outlet 17 of the collector to the inlet 12 of thecondenser and a conduit 21 connects the outlet 13 of the condenser tothe inlet 16 of the collector. The condenser 11, the conduit 21, thecollector 15, and the conduit 19 form a closed circuit and thephase-change liquid heat transfer medium 22 is located within the closedcircuit. An accumulator 23 is provided, having a means 24 for regulatingthe pressure within it and having an inlet 25 that is connected to thecircuit below the condenser 11; specifically, it is connected adjacentthe inlet 16 of the collector 15. A vapor-release drum 26 is connectedin the circuit between the outlet 17 of the solar collector 15 and theinlet 12 of the condenser 11.

Referring particularly to FIG. 2, it can be seen that the vapor-releasedrum 26 has sufficient volume to assure that the upper surface 27 of theheat-transfer medium 22 always remains within the confines of the drumduring normal operation of the heater. The solar collector 15 has agenerally rectangular configuration with an upper horizontal edge 28 onwhich the collector outlet 17 is located. The vapor-release drum has anelongated cylindrical configuration that extends parallel to and isspaced upwardly from the said upper horizontal edge of the solarcollector. The heat transfer medium 22 in the preferred embodiment is afluorinated hydrocarbon, specifically, Freon 114. The drum 26 isprovided with a liquid level observation window 34. The drum 26 is ofelongated cylindrical confirmation and is initially supplied forincorporation into the circuit with integral nipples 37 for fieldconnection to the conduit.

The accumulator 23 is of the bladder-type and its bladder 29 is formedof Neoprene or butyl rubber. The condenser 11 is located within aninsulated water tank 31 containing the body of water 14 and the watertank has a lower water inlet 32 and an upper water outlet 33. Thecondenser 11 and the tank 31 are formed of stainless steel for lightnessand resistance to corrosion.

The solar collector 15, the conduits 19 and 21, the drum 26, and thecondenser 11 are arranged so that no vapor traps exist within them whichwould restrict the flow of vapor. In the preferred embodiment, thevarious conduits, including the conduits 19 and 21, are formed fromdeoxidized copper tubing and deoxidized forging copper fittings whichare silver soldered with a forming-gas atmosphere and a hydrogen torch.

A shut-off valve 35 is located adjacent the accumulator inlet 25 topermit it to be disconnected from the circuit without loss of pressureor fluid. The accumulator 23 is capable of independently containing asupply of liquid under pressure before initial installation, because ofthe presence of this valve. The accumulator 23 consists of a containerseparated into two parts by the flexible bladder 29, the container beingprovided with a valve inlet at the one part for the introduction andretention of an inert gas under pressure with a valve inlet at the otherpart for the introduction and retention of the heat-exchange fluid.

The operation of the solar water heater 10 will now be readilyunderstood in view of the above description. Its installation at thesite is facilitated by the fact that the accumulator 23 can be shippedas an independent unit with the heat-exchange fluid initially underpressure, so that it is not necessary to deliver pressurizing equipmentto the site. Also the drum element, as has been stated, is provided withnipples 37 and 38 which are readily attached to the other element; forinstance, the nipples 37 are attached to the outlet pipes 17 of thecollector 15 and the nipple 38 can be attached to the conduit 19 leadingto the inlet 12 of the condenser 11. Normally, the collector 15 would bemounted in an inclined condition, as shown in FIG. 2, and directedtoward the sun with an angularity determined by the direction of thepath of the sun during various parts of the year. The condenser, ofcourse, must be provided at a higher point and quite often can belocated in the peak of the roof of the building within which theapparatus is to be used.

During operation, the heat-exchange medium or fluid 22 in the collector15 is subjected to heat from the sun's rays and its temperature rises.Eventually, the temperature of vaporization at the particular pressureselected is reached and the fluid in the upper, warmer part of the bodyvaporizes. It leaves the surface 27 in the form of bubbles and passesinto the portion of the drum 26 above the liquid level. The vapor passesthrough the conduit 19 into the entrance 12 of the condenser 11. Withinthe water tank 31 and the body of water 14, the condenser is providedwith inclined heat-exchange units facilitating the transfer byconduction of heat from the heat-exchange vapor into the water. Thewater forms part of a flowing hot water circuit (not shown) which isexternal of the apparatus, but including inlet 32 and outlet 33. Theconduction of heat into the body of water causes the temperature of thevapor to drop until the condensation point is reached. The liquid thusformed flows out of the condenser through the outlet 13, down to conduit21, and to the bottom of the collector 15. At the bottom part of thecollector, the liquid enters the collector through the inlets 16 and thecycle is continuously repeated. The pressure in the system is limited toa pre-set value by the accumulator 23 and by the means 24 for regulatingthe pressure which operates through the valve inlet 36 of theaccumulator on one side of the bladder 29, the heat-exchange fluid beingon the other side.

The advantages of the invention will now be readily understood in viewof the above description. The drum 26 acts as a reservoir to maintain anadequate level of liquid Freon without flooding the heat-exchanger orcondenser 11. It provides an increased surface to act as a velocityreducer and provides positive separation of the vapor from the liquid toprevent carry-over of the liquid into the condenser. The presence of thevapor-release drum 26 also serves as a damper to prevent the oscillatoryaction which would cause the level of the liquid to oscillate and causecarry-over of liquid into the heat-exchanger. It will be understood thatthe presence of liquid in the heat-exchanger reduces the efficiency ofthe phase-change heat transfer, since the most desirable situation isfor all heat transfer to take place due to the large calorie value ofthe conversion of the vapor to the liquid phase. This calorie value isthe so-called "heat of vaporization" and is much larger than the heatavailable by simple temperature reduction of the liquid. The presence inthe circuit of the drum 26 and its observation window 34 permits theoperator to observe and assure that the liquid level is within theproper level, that is to say, that the surface 27 of the liuqid body 22remains in the same place, and so that he can make adjustments if it isnot. The use of the prefabricated drum 26 makes installation much easierand reduces cost. The precharged accumulator 23 greatly reduces initialequipment required at the installations site and also reduces the degreeof skilled labor that is necessary. The system shown in the drawing alsoprovides a means for storing the Freon in the accumulator, whileperforming repairs or replacement of components in the system and thiscan be done without releasing the Freon into the atmosphere. It alsoprovides a means for recovering the Freon, if the system is dismantled,without the use of any special recovery equipment and it avoids therelease of Freon into the atmosphere which is desirable from anecological point of view. The means 24 for regulating the pressure inthe accumulator is shown as a pressurized tank of gas in the preferredembodiment an inert gas such as nitrogen, carbondioxide, or argon isused to improve the reliability for the accumulator in the system andassures that deterioration of the equipment due to the chemical attackdoes not take place. The present system allows for the geographicplacement of the accumulator anywhere in the system, as long as it isconnected to the lowest point in the system.

It can be seen that the present system allows a wood-burning system tobackup the heat by using it in parallel with the heat-exchanger or tank31, the collectors acting as a thermal diode. The present system alsomakes it possible to use a dual orientation for the solar collector 15,possibly by bringing about a facing of the collectors southeast tocollect the maximum heat output at 9 A.M. and toward the southwest forthe maximum heat output at 3 P.M. and also to better match the water usewithout the need for any additional controls.

It is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include allsuch as properly come within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:
 1. Solar water heater making useof phase-change heat transfer, comprising:(a) a condenser having an.Iadd.upper .Iaddend.inlet and .[.an.]. .Iadd.a lower .Iaddend.outlet,which condenser is in contact with the water to be heated, (b) a solarcollector having a bottom inlet and a top outlet and .[.having an.]..Iadd.at least one .Iaddend.inner conduit that connects the inlet andthe outlet, the conduit being suitable for exposing a heat-transfermedium .[.in.]. .Iadd.within the length of .Iaddend.the conduit to solarenergy, the collector outlet being located below the condenser, (c).[.conduits joining.]. .Iadd.a second conduit connecting .Iaddend.theoutlet of the collector .Iadd.directly .Iaddend.to the inlet of thecondenser and .Iadd.a third conduit connecting .Iaddend.the outlet ofthe condenser directly to the inlet of the collector to form a closedcircuit, .[.(d) A.]. .Iadd.said closed circuit adapted to be chargedwith a .Iaddend.phase-change .[.liquid.]. heat transfer medium.[.located within the circuit.]., .Iadd. (d) means for limiting thepressure in said closed circuit during normal operation of the heater,and .[.(e) an accumulator having means for regulating the pressuretherein and having an inlet that is connected to the circuit below thecollector, and.]. .[.F.]. (.Iadd.e.Iaddend.) a vapor-release drumconnected in the circuit .[.between the outlet of the solar collectorand the inlet of the condenser.]., .Iadd.upstream of said condenser anddownstream of said inner conduit, said inner conduit having its outletat a point in said drum which is during normal operation of the heaterbelow the liquid-vapor interface within said drum so as to receive heattransfer medium from said inner conduit and, .Iaddend.wherein thevapor-release drum has sufficient volume that the upper surface of theheat transfer medium .[.always.]. remains within the confines of thedrum so that, during normal operation of the heater only the heattransfer medium which becomes vaporized is released into the inlet ofthe condenser .Iadd.whereby all heat transfer takes place due to theconversion of the vapor to the liquid phase.Iaddend.. .[.2. Solar waterheater as recited in claim 1, wherein the solar collector has agenerally rectangular configuration with an upper horizontal edge onwhich the collector outlet is located, and wherein the vapor-releasedrum has an elongated cylindrical configuration that extends parallel toand spaced upwardly from the said upper horizontal edge of the solarcollector..]. .[.3. Solar water heater as recited in claim 2, whereinthe heat transfer medium is a fluorinated hydrocarbon..]. .[.4. Solarwater heater as recited in claim 3, wherein the heat transfer medium isFreon 114..].
 5. Solar water heater as recited in claim 1, wherein.[.the accumulator is a bladder-type.]. .Iadd.said means for limitingpressure in said closed circuit comprises a bladder-type accumulatorhaving means for regulating the pressure therein and having an inletthat is connected to the circuit below the collector.Iaddend.. .[.6.Solar water heater as recited in claim 5, wherein the bladder is formedof Neoprene..].
 7. Solar water heater as recited in claim 1, wherein thecondenser is located within an insulated water tank, the water tankhaving a lower water inlet and an upper water outlet the condenser andtank being formed of stainless steel. .[.8. Solar water heater asrecited in claim 1, wherein the solar collector, the conduits, the drum,and the condenser are arranged so that no vapor traps exist within themwhich would restrict the flow of vapor..]. .[.9. Solar water heater asrecited in claim 1, wherein the conduits are comprised of deoxidizedcopper tubing and deoxidized forged copper fittings which are silversoldered..]. .[.10. Solar water heater as recited in claim 1, whereinthe drum is provided with a liquid level observation window..]. Solarwater heater as recited in claim .[.1.]. .Iadd.5 .Iaddend.wherein ashut-off valve is located adjacent the accumulator inlet to permit it tobe disconnected from the circuit without loss of pressure or of fluid.12. Solar water heater as recited in claim 11, wherein the accumulatoris capable of independently containing a supply of fluid under pressurebefore initial installation.
 13. Solar water heater as recited in claim.[.11.]. .Iadd.5.Iaddend., wherein the accumulator consists of acontainer separated into two parts by a flexible bladder, the containerbeing provided with a valved inlet into one part for the introductionand retention of an inert gas under pressure and with a valved inletinto the other part for the introduction and retention of the fluid..[.14. Solar water heater as recited in claim 1, wherein the drum is ofelongated cylindrical conformation and is initially charged with theheat transfer fluid before incorporation into the circuit with integralnipples for field-connection to the conduits..].